As automotive continuously variable belt and pulley transmissions, for example, a continuously variable belt and pulley transmission is known that is described in Japanese Patent Unexamined Publication No. JP-A-8-30526.
Such a continuously variable belt and pulley transmission has an input-side rotational shaft 1 and an output-side rotational shaft 2 which are disposed in parallel with each other. The input-side rotational shaft 1 is driven to rotate by an engine 3 via a torque converter 4 and a starter clutch, which is an electromagnetic clutch or the like. Then, the rotation of the output-side rotational shaft 2 is transmitted to a pair of left and right drive wheels 10 via a speed reduction gear train 8 and a differential gear 9.
These input-side rotational shaft 1 and output-side rotational shaft 2 are each supported rotatably by a pair of roller bearings 5, 6 within a transmission case, not shown.
A drive-side pulley 11 is provided at an intermediate portion of the input-side rotational shaft 1, so that the drive-side pulley 11 and the input-side rotational shaft 1 are designed to rotate in synchronism with each other. The space between a pair of drive-side pulley plates 12, 12 which make up the drive-side pulley 11 can be adjusted freely by means of a drive-side displacement unit, not shown. Namely, the width of a raceway groove in the drive-side pulley 11 can freely be widened and narrowed by means of this drive-side displacement unit.
In addition, a driven-side pulley 13 is provided at an intermediate portion of the output-side rotational shaft 2, so that the driven-side pulley 13 and the output-side rotational shaft 2 are designed to rotate in synchronism with each other. The space between a pair of driven-side pulley plates 14, 14 which make up the driven-side pulley 13 can be adjusted freely by means of a driven-side displacement unit, not shown. Namely, the width of a raceway groove in the driven-side pulley 13 can freely be widened and narrowed by means of this driven-side displacement unit. Then, an endless belt 15 is extended between the driven-side pulley 13 and the drive-side pulley 11.
In the variably continuous belt and pulley transmission that is configured as has been described heretofore, power that has been transmitted from the engine to the input-side rotational shaft 1 via the torque converter 4 and the starter clutch is then transmitted to the driven-side pulley 13 from the drive-side pulley 11 via the endless belt 15.
Note that as this endless belt 15, there are known an endless belt which transmits power in compression and an endless belt which transmits power under tension. In either case, the power that has been transmitted to the driven-side pulley 13 is transmitted from the output-side rotational shaft 2 to the drive wheels 10 via the speed reduction gear train 8 and the differential gear 9.
Then, when the speed ratio between the input-side rotational shaft 1 and the output-side rotational shaft 2 is changed, the raceway grooves of the drive-side pulley 11 and the driven-side pulley 13 are widened and/or narrowed in relation to each other.
For example, when the speed ratio between the input-side rotational shaft 1 and the output-side rotational shaft 2 is increased, the width of the raceway groove of the drive-side pulley 11 is increased, whereas the width of the raceway groove of the driven-side pulley 13 is narrowed. As a result, the wrap contact diameters of portions of the endless belt 15 which are wound around the drive-side pulley 11 and the driven-side pulley 13 change in such a manner that the wrap contact diameter of the portion of the endless belt 15 which is wound around the drive-side pulley 11 is decreased, whereas the wrap contact diameter of the portion of the endless belt 15 which is wound around the driven-side pulley 13 is increased, whereby a speed reduction is implemented between the input-side rotational shaft 1 and the output-side rotational shaft 2.
In contrast, when the speed increase ratio between the input-side rotational shaft 1 and the output-side rotational shaft 2 is increased (the speed reduction ratio is decreased), the width of the raceway groove of the drive-side pulley 11 is narrowed, whereas the width of the raceway groove of the driven-side pulley 13 is widened.
In the continuously variable belt and pulley transmission that is configured as has been described heretofore, in order to realize a low fuel consumption by increasing to stabilize the friction coefficient between the metallic endless belt and pulleys, while lubrication is implemented using a CVT fluid (a fluid that double as an AFT) with 100 cc/min or greater, since there is a high possibility that wear dust resulting from the frictional contact between the endless belt and the pulleys and gear dust enter the roller bearings which support the pulleys, the size of the bearings is increased or the diameter of the rolling element is increased, and a bearing needs to be designed in which the basic kinematic rated load is increased using, for example, a roller bearing.
Incidentally, in the utilization of a cylindrical roller bearing, generally, in order to prevent the generation of edge load, a crowning is applied to a raceway surface of a cylindrical roller or raceway surfaces of bearing rings. As a crowning like this, there are known a full crowning in which a generator of the rolling surface or raceway surface is made into an arc with a constant curvature, a trapezoidal crowning in which a taper surface which recedes away from the raceway surface (the rolling surface) is formed at each edge portion of the rolling surface (or the raceway surface) and a logarithmic crowning in which the generator of the rolling surface of the raceway surface is made into a logarithmic curve.
For example, Japanese Utility Model Unexamined Publication No. JP-UM-A-5-22845 discloses a roller bearing is disclosed in which a number of rollers are provided rollably between inner and outer bearing rings, the rollers are brought into line contact with the respective bearing rings, and guide collars are formed at both edges of one of the bearing rings, as well as a technique in which a trapezoidal crowning is formed on a raceway surface of the bearing ring which is provided with the guide collars by applying crowning to both collar sides of the raceway surface of the bearing ring except for a central straight line portion thereof, and a full crowning is applied to a raceway surface of the other bearing ring which is provided with no guide collar.
In addition, Japanese Patent Unexamined Publication No. JP-A-2001-124089 discloses a technique in which in order to equalize stress on the rolling surface of a cylindrical roller, a crowning is applied to the rolling surface of the cylindrical roller in which a drop amount Y at an arbitrary position is expressed as a function of an axial distance X from an axial center M to the arbitrary position {Y=AXB (A, B denote arbitrary numbers)}, and the axial length L1 of an area where the drop amount Y becomes 5 μm or smaller (Y1) is set to 50% or greater of the axial length L0 of the cylindrical roller, and furthermore a maximum value Y0 of the drop amount Y is set to 0.15% or greater of the axial length L0 of the cylindrical roller.
However, when a full crowning and a trapezoidal crowning are applied to the raceway surface and the rolling surface of the roller in a general cylindrical roller bearing, there occurs a problem that in the event that the crowning is enlarged in order to prevent an edge load that is generated when the bearing rings and the cylindrical rollers are inclined due to a moment of larger magnitude acting on the bearing, the load capacity is decreased.
In addition, in the case of the logarithmic crowning, since the configuration is complex, there is caused a problem that the machining becomes difficult and hence costs are increased.
Furthermore, while an outer ring, an inner ring and roller elements of a standard bearing steel of classification 2 (SUJ2) are used in each of the roller bearings that are incorporated in the aforesaid continuously variable belt and pulley transmission, there exists a tendency to use a CVT fluid with low viscosity in order to secure the efficiency (low fuel consumption) of the continuously variable belt and pulley transmission, keep the level of noise generated during driving to a lower level, and suppress the wear of the drive-side and driven-side pulleys and the endless belt.
Then, in rolling bearings using the standard bearing steel of classification 2, it is considered that not a dent originating type flaking, which is generated by inclusion of foreign matters caused by vibrations generated in association with change in belt, but a premature flaking is generated by virtue of the occurrence of metal contact between the bearing rings and the roller elements that results from rotation slippage, revolution slippage, differential slippage and skew.
This is because since a CVT fluid with low viscosity (the basic oil kinematic viscosity is 40 mm2/sec or smaller at 40°, 10 mm2/sec or smaller at 100° C.) is used as a lubricating oil under an environment in which the bearing temperature exceeds 100° C., it is anticipated that the amount of lubrication in the interior of the bearing is equal to or less than what is assumed (insufficient lubrication), resulting in chronic formation of insufficient oil film.
In addition, since the transmission case of a continuously variable belt and pulley transmission has a low housing rigidity, an oil film failure occurs between the roller element and the surface of the raceway due to the effect of the aforesaid slippages in association with the deformation of the raceway surface of the outer ring, and the raceway surface becomes activated, whereby by virtue of the intrusion of, for example, hydrogen, a hydrogen-attributed brittle flaking and a surface fatigue in association with the metal contact are promoted, leading to a problem that a premature flaking occurs.
Consequently, even with the specification, being the advantage and object of JP-UM-A-5-22845 and JP-A-2001-124089, in which in a utilizing condition where the inner and outer rings have a relative inclination angle, since the application of appropriate crowning to the raceway surfaces of the inner and outer rings eliminates the occurrence of edge load and excludes a numerical restriction to a single curvature, prying generated at edge surfaces of the roller is not generated at the guide collars, as well, there can be provided no countermeasures against the premature flaking that occurs on roller bearings for continuously variable belt and pulley transmissions.
Consequently, the invention was made in view of these situations, and an object thereof is to prove a roller bearing for continuously variable belt and pulley transmissions which can realize a continuously variable belt and pulley transmission which provides a low fuel consumption and has a superior transmission efficiency and a sufficient durability.